1. Field of the Invention
The invention relates to the use of cross-linkable, redipersible dispersion powders based on vinyl ester copolymers or (meth)acrylic acid ester copolymers as binders for dry binding of fibre materials.
To increase resistance to mechanical stress, fibre structures are compacted with binders. These binders can be used in the form of solids, such as powders, granules or fibres, or as liquids, such as solutions or dispersions. The increased strength results from binding of the fibres by the polymers, which adhere to the fibre and in this way reinforce the fibre structures.
2. Background Art
A procedure is known from WO-A 90/14457 in which, after a carding step, glass fibres are mixed with a thermoplastic powder, for example polypropylene, polyester or polyamide, and the fibre structure is then compacted at elevated temperature and under pressure. AU-B 36659/89 also describes the compaction of glass fibre materials by means of thermoplastic powders. The use of polyesters or polystyrene is recommended here. A disadvantage is the low strength of the fibre structures thus bonded in contact with water or solvents.
If fibre non-wovens of increased strength, above all in contact with water or solvents or at elevated temperature, are to be obtained, polymers which can crosslink or polymerize completely in a particular processing step are employed. EP-B 0080144 (U.S. Pat. No. 4,451,315) describes the compaction of fibre non-wovens of polyester, polyamide or cotton fibres with emulsions of self-crosslinking acrylic ester copolymers, ethylene/vinyl acetate copolymers or self-crosslinking synthetic rubbers. Non-woven materials of high strength are indeed obtained by this process; the disadvantage of using aqueous binders, nevertheless, is the high drying expenditure; furthermore, distribution of the binder in the fibre matrix is problematic.
The compaction of pulverulent, crosslinkable polymers based on phenol-formaldehyde resins is described in U.S. Pat. No. 4,612,224. The disadvantage of this binder system is the high formaldehyde emission during preparation and use of the fibre materials thus compacted.
The invention was based on the object of providing binders for compaction of fibre materials which can be employed as powders and have a high wet strength and good heat stability, avoiding harmful emissions during processing.
The object has been achieved by the development of a dry binder based on thermoplastic copolymers which have only small contents of comonomers which have a crosslinking action and nevertheless effect a high strength coupled with a negligible formaldehyde emission.
Thermosetting copolymers based on acrylic acid esters and/or vinyl esters, which also comprise (meth)acrylic acid esters of mono- or polyfunctional hydroxy-carboxylic acids and N-alkoxyalkyl(meth)acrylamide as crosslinking components, are described as pulverulent paints in DE-A-2701490 (U.S. Pat. No. 4,129,545).